A top-down strategy for amorphization of hydroxyl compounds for electrocatalytic oxygen evolution

Electron-phonon coupling and coherent energy superposition induce spin-sensitive orbital degeneracy for enhanced acidic water oxidation

The development of acid-stable water oxidation electrocatalysts is crucial for high-performance energy conversion devices. Different from traditional nanostructuring, here we employ an innovative microwave-mediated electron-phonon coupling technique to assemble specific Ru atomic patterns (instead of random Ru-particle depositions) on Mn0.99Cr0.01O2 surfaces (RuMW-Mn1-xCrxO2) in RuCl3 solution because hydrated Ru-ion complexes can be uniformly activated to replace some Mn sites at nearby Cr-dopants through microwave-triggered energy coherent superposition with molecular rotations and collisions. This selective rearrangement in RuMW-Mn1-xCrxO2 with particular spin-differentiated polarizations can induce localized spin domain inversion from reversed to parallel direction, which makes RuMW-Mn1-xCrxO2 demonstrate a high current density of 1.0 A cm-2 at 1.88 V and over 300 h of stability in a proton exchange membrane water electrolyzer. The cost per gallon of gasoline equivalent of the hydrogen produced is only 43% of the 2026 target set by the U.S. Department of Energy, underscoring the economic significance of this nanotechnology.

Beyond conventional structures: emerging complex metal oxides for efficient oxygen and hydrogen electrocatalysis

The core of clean energy technologies such as fuel cells, water electrolyzers, and metal-air batteries depends on a series of oxygen and hydrogen-based electrocatalysis reactions, including the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), which necessitate cost-effective electrocatalysts to improve their energy efficiency. In the recent decade, complex metal oxides (beyond simple transition metal oxides, spinel oxides and ABO3 perovskite oxides) have emerged as promising candidate materials with unexpected electrocatalytic activities for oxygen and hydrogen electrocatalysis owing to their special crystal structures and unique physicochemical properties. In this review, the current progress in complex metal oxides for ORR, OER, and HER electrocatalysis is comprehensively presented. Initially, we present a brief description of some fundamental concepts of the ORR, OER, and HER and a detailed description of complex metal oxides, including their physicochemical characteristics, synthesis methods, and structural characterization. Subsequently, we present a thorough overview of various complex metal oxides reported for ORR, OER, and HER electrocatalysis thus far, such as double/triple/quadruple perovskites, perovskite hydroxides, brownmillerites, Ruddlesden-Popper oxides, Aurivillius oxides, lithium/sodium transition metal oxides, pyrochlores, metal phosphates, polyoxometalates and other specially structured oxides, with emphasis on the designed strategies for promoting their performance and structure-property-performance relationships. Moreover, the practical device applications of complex metal oxides in fuel cells, water electrolyzers, and metal-air batteries are discussed. Finally, some concluding remarks summarizing the challenges, perspectives, and research trends of this topic are presented. We hope that this review provides a clear overview of the current status of this emerging field and stimulate future efforts to design more advanced electrocatalysts.

Amorphous Pd nanoparticles inside ethylenediamine-based nanocomposite for high N2-selectivity of nitrate reduction

Catalytic reduction of nitrate to dinitrogen (N2) by noble metals stands as a feasible and promising manner to address the biological and environmental issues associated with nitrate pollution; however, nitrate reduction under single noble-metal catalyzation remains substantially stuck because of the low adsorption enthalpy of noble metal toward nitrate. Tailoring the formation (crystal structure and particle size) of catalytical metal particles, coupled with a more direct electron donating pattern, provides a potential solution for the main challenge in reduction efficiency and selectivity. In this study, we assembled a Pd-based nanocomposite (Pda@EC) by subtly regulating the embedded Pd nanoparticles inside a porous substrate self-sufficient in electron donator (i.e., ethylenediamine group, EDA). Without any provision of reductant, the resultant single-metal catalyst demonstrated excellent nitrate catalytic reduction with over 95 % of N2 reduction selectivity within very broad pH range (3-11), whereas its unregulated counterpart (crystal Pd nanocomposite, Pdc@EC) is incapable of efficient nitrate reduction under otherwise identical conditions. The activated hydrogen (H*), which was exclusively yielded under the catalyzation of the amorphous Pd nanoparticles for the electron donating EDA, was confirmed as the primary active species, and the high N2 selectivity is attributed to the cooperation between EDA and Pd nanoparticles. More promisingly, the exhausted Pda@EC is amenable to effective regeneration with mild NaOH (elution) and NaBH4 (restoration) treatment. This work provides an effective strategy for selectively reducing nitrate under monometallic catalyzation by subtly regulating the crystal structure of Pd nanoparticles in endogenous electron-donating environment.

Tracking the correlation between spintronic structure and oxygen evolution reaction mechanism of cobalt-ruthenium-based electrocatalyst

Regulating the spintronic structure of electrocatalysts can improve the oxygen evolution reaction performance efficiently. Nonetheless, the effects of tuning the spintronic structure for the oxygen evolution reaction mechanisms have rarely been discussed. Here, we show a ruthenium-cobalt-tin oxide with optimized spintronic structure due to the quantum spin interaction of Ru and Co. The specific spintronic structure of ruthenium-cobalt-tin oxide promotes the charge transfer kinetics and intermediates evolution behavior under applied potential, generating long-lived active species with higher spin density sites for the oxygen evolution reaction after the reconstruction process. Moreover, the ruthenium-cobalt-tin oxide possesses decoupled proton-electron transfer procedure during the oxygen evolution reaction process, demonstrating that the electron transfer procedure of O-O bond formation between *O intermediate and lattice oxygen in Co-O-Ru is the rate-determining step of the oxygen evolution reaction process. This work provides rational perspectives on the correlation between spintronic structure and oxygen evolution reaction mechanism.

Selective conversion of thermal decomposition products of ammonium perchlorate by amorphous CoSnOx

The directional transformation of products in the multiphase decomposition process of ammonium perchlorate (AP) still faces significant challenges, one of which is the conversion of greenhouse gas N2O. Furthermore, additional elucidation of the structure and potential catalytic mechanisms of catalysts with high thermal stability is imperative for the aforementioned process. This study proposes a cobalt-based amorphous oxide with high thermal stability for catalysing the thermal decomposition of AP and achieving the transformation of catalytic products from N2O to NO (and its derivatives). The results indicate that the type of catalytic decomposition products is related to the structural transformation of the catalyst, suggesting a synergistic oxidation mechanism by active oxygen and lattice oxygen. The peak decomposition temperature of AP has dropped to near the limit of 257.2 °C, TG-IR test and MD simulation results indicate the selective generation of NO under the lattice oxygen mechanism. In addition, kinetic calculations elucidated the transition of catalysts from amorphous to crystalline state in catalysis. Finally, suggestions were made for the current characterization techniques of catalysts. This study offers a reference point for the catalyst design of AP decomposition-oriented products, which is beneficial for the transition to more environmentally-friendly products.

Manipulating the d- and p-Band centers of amorphous alloys by variable composition for robust oxygen evolution reaction

Amorphous electrocatalysts display several unique advantages in electricity-driven water splitting compared to their crystalline analogs, but understanding their structure-activity relationships remains a major challenge. Herein, we show that the d- and p-electronic states of amorphous Ni-Fe-B can be subtly manipulated by varying the Ni and Fe contents. The optimal Ni-Fe-B alloy exhibits a high performance in the oxygen evolution reaction (OER), as supported by its impressive stability (no clear degradation after 100 h) and considerably lower overpotential compared to those of its crystalline analogs. Based on theoretical calculations, different Ni and Fe contents can cause significant shifts in the d-band levels of Ni and Fe and the p-band level of B, thus altering the OER activity. Additionally, the energy difference between the d- and p-band centers (ΔEad-p) may be an effective index for use in reflecting the structure-activity relationship of an amorphous Ni-Fe-B alloy in the OER. An amorphous Ni-Fe-B alloy with a smaller ΔEad-p displays a higher intrinsic activity. This study supplies a unique direction for use in constructing the structure-activity relationships of amorphous electrocatalysts by revealing the role of ΔEad-p, which promotes fundamental research and the practical application of amorphous electrocatalysts.

Solvation Effect-Determined Mechanisms of Cation Exchange Reactions for Efficient Multicomponent Nanocatalysts

Cation exchange (CE) reaction is a classical synthesis method for creating complex structures. A lock of study on intrinsic mechanism limits its understanding and practical application. Using X-ray absorption spectroscopy, we observed that the evolution from Ru-Cl to Ru-O/OH occurs during the CE between K2RuCl6 and CoSn(OH)6 in aqueous solution, while CE between K2PtCl6 and CoSn(OH)6 is inhibited due to the failure of structural evolution from Pt-Cl to Pt-O/OH. Theoretical simulations imply that the interaction between Ru-O and CoSn(OH)6 with Co vacancy (CoVCoSn(OH)6) endows the electron transfer, as a result of strengthened adsorption on CoVCoSn(OH)6. Moreover, this mechanism is validated for CE between K2RuCl6 and ASn(OH)6 (A=Mg, Ca, Mn, Co, Cu, Zn), and CE between K2PdCl6/Na3RhCl6/K2IrCl6 and CoSn(OH)6. Impressively, the Pt-free CoRuSn(OH)x produced via CE displays a mass activity and a power density of 15.0 A mgRu -1 and 11.6 W mgRu -1, respectively, for anion exchange membrane fuel cell (AEMFC) exceeding the values of commercial PtRu/C (11.8 A mgRu+Pt -1 and 9.0 W mgRu+Pt -1). This work, for the first time, reveals the intrinsic mechanism of CE as structural evolution of target ion breaking through the traditional classic etch-adsorption mechanism and will promote fundamental research and practical application in various fields.

Concurrent Amorphization and Nanocatalyst Formation in Cu-Substituted Perovskite Oxide Surface: Effects on Oxygen Reduction Reaction at Elevated Temperatures

The activity and durability of chemical/electrochemical catalysts are significantly influenced by their surface environments, highlighting the importance of thoroughly examining the catalyst surface. Here, Cu-substituted La0.6Sr0.4Co0.2Fe0.8O3-δ is selected, a state-of-the-art material for oxygen reduction reaction (ORR), to explore the real-time evolution of surface morphology and chemistry under a reducing atmosphere at elevated temperatures. Remarkably, in a pioneering observation, it is discovered that the perovskite surface starts to amorphize at an unusually low temperature of approximately 100 °C and multicomponent metal nanocatalysts additionally form on the amorphous surface as the temperature raises to 400 °C. Moreover, this investigation into the stability of the resulting amorphous layer under oxidizing conditions reveals that the amorphous structure can withstand a high-temperature oxidizing atmosphere (≥650 °C) only when it has undergone sufficient reduction for an extended period. Therefore, the coexistence of the active nanocatalysts and defective amorphous surface leads to a nearly 100% enhancement in the electrode resistance for the ORR over 200 h without significant degradation. These observations provide a new catalytic design strategy for using redox-dynamic perovskite oxide host materials.

Modulating the Electronic Structure of Cobalt-Vanadium Bimetal Catalysts for High-Stable Anion Exchange Membrane Water Electrolyzer

Modulating the electronic structure of catalysts to effectively couple the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for developing high-efficiency anion exchange membrane water electrolyzer (AEMWE). Herein, a coral-like nanoarray composed of nanosheets through the synergistic layering effect of cobalt and the 1D guiding of vanadium is synthesized, which promotes extensive contact between the active sites and electrolyte. The HER and OER activities can be enhanced by modulating the electronic structure through nitridation and phosphorization, respectively, enhancing the strength of metal-H bond to optimize hydrogen adsorption and facilitating the proton transfer to improve the transformation of oxygen-containing intermediates. Resultantly, the AEMWE achieves a current density of 500 mA cm-2 at 1.76 V for 1000 h in 1.0 M KOH at 70 °C. The energy consumption is 4.21 kWh Nm-3 with the producing hydrogen cost of $0.93 per kg H2. Operando synchrotron radiation and Bode phase angle analyses reveal that during the high-energy consumed OER, the dissolution of vanadium species transforms distorted Co-O octahedral into regular octahedral structures, accompanied by a shortening of the Co-Co bond length. This structural evolution facilitates the formation of oxygen intermediates, thus accelerating the reaction kinetics.

Amorphous ZnSnOx Hollow Spheres Enable Highly Efficient CO2 Reduction

Carbon dioxide (CO2) adsorption and electron transport play an important role in CO2 reduction reaction (CO2RR). Herein, we have demonstrated a new class of diverse hollow ZnSnOx (ZSO) through the amorphization of hydroxides to enhance CO2 adsorption and accelerate electron transport. The amorphization is occurred by calcination process, as indicated by Fourier transform infrared spectroscopy and Raman spectra. In particular, the ZnSnOx hollow spheres (ZSO HSs) achieve a high Faradaic efficiency (FE) of HCOOH up to 92.7 % at best, outperforming the commercial ZSO (Comm. ZSO, 85.7 %). ZSO HSs also exhibit durable stability with negligible activity decay after 10 h of successive electrolysis. In-situ attenuated total reflectance infrared absorption spectroscopy further reveals strong adsorption of CO2 and rapid intermediate configuration transformation in amorphous ZSO HSs. This work demonstrates the practical application of ZSO for CO2RR and provides a new insight to create efficient CO2RR electrocatalysts.

Amorphous/Crystalline Phases Mixed Nanosheets Array Rich in Oxygen Vacancies Boost Oxygen Evolution Reaction of Spinel Oxides in Alkaline Media

As promising oxygen evolution reaction (OER) catalysts, spinel-type oxides face the bottleneck of weak adsorption for oxygen-containing intermediates, so it is challenging to make a further breakthrough in remarkably lowering the OER overpotential. In this study, a novel strategy is proposed to substantially enhance the OER activity of spinel oxides based on amorphous/crystalline phases mixed spinel FeNi2O4 nanosheets array, enriched with oxygen vacancies, in situ grown on a nickel foam (NF). This unique architecture is achieved through a one-step millisecond laser direct writing method. The presence of amorphous phases with abundant oxygen vacancies significantly enhances the adsorption of oxygen-containing intermediates and changes the rate-determining step from OH*→O* to O*→OOH*, which greatly reduces the thermodynamic energy barrier. Moreover, the crystalline phase interweaving with amorphous domains serves as a conductive shortcut to facilitate rapid electron transfer from active sites in the amorphous domain to NF, guaranteeing fast OER kinetics. Such an anodic electrode exhibits a nearly ten fold enhancement in OER intrinsic activity compared to the pristine counterpart. Remarkably, it demonstrates record-low overpotentials of 246 and 315 mV at 50 and 500 mA cm-2 in 1 m KOH with superior long-term stability, outperforming other NiFe-based spinel oxides catalysts.

Strong Carbon Layer-Encapsulated Cobalt Tin Sulfide-Based Nanoporous Material as a Bifunctional Electrocatalyst for Zinc-Air Batteries

Global demands for cost-effective, durable, highly active, and bifunctional catalysts for metal-air batteries are tremendously increasing in scientific research fields. In this work, a strategy for the rational fabrication of carbon layer-encapsulated cobalt tin sulfide nanopores (CoSnOH/S@C NPs) material as a bifunctional electrocatalyst for rechargeable zinc (Zn)-air batteries by a cost-effective and facile two-step hydrothermal method is reported. Moreover, the effect of metal elements on the morphology of CoSnOH nanodisks material via the hydrothermal method is investigated. Owing to its excellent nanostructure, exclusive porous network, and high specific surface area, the optimized CoSnOH/S@C NPs material reveals superior catalytic properties. The as-prepared CoSnOH/S@C NPs electrocatalyst reveals better properties of oxygen reduction reaction (half-wave potential of -0.88 V vs reversible hydrogen electrode) and oxygen evolution reaction (overpotential of 137 mV at 10 mA cm-2) when compared with commercial Pt/C and IrO2 catalyst materials. Most significantly, the CoSnO/S@C NPs-based Zn-air battery exhibits more excellent cycling stability than the Pt/C+IrO2 catalyst-based one. Consequently, the proposed material provides a new route for fabricating more active and stable multifunctional catalyst materials for energy conversion and storage systems.

Directional Activation of Oxygen by the Au-Loaded ZnAl-LDH with Defect Structure for Highly Efficient Photocatalytic Oxidative Coupling of Methane

Photocatalytic oxidative coupling of CH4 (OCM) is a promising CH4 conversion process that can achieve efficient methane conversion with the assistance of O2. It remains to be highly challenging to improve the photocatalytic OCM activity from catalyst design and to deepen the understanding of the reactant activation in the OCM process. In this work, the Au-loaded ZnAl-layered double hydroxides (LDHs) with and without oxygen vacancy are constructed (denoted as Au/ZnAl and Au/ZnAl-v), respectively. When applied for photocatalytic OCM, the Au/ZnAl-v shows a CH4 conversion rate of 8.5 mmol g-1 h-1 with 92% selectivity of C2H6 at 40 °C, outperforming most reported photocatalytic OCM systems at low temperature reported in the literature. Furthermore, the catalytic performance of Au/ZnAl-v can be stable for 100 h. In contrast, the An/ZnAl exhibits a CH4 conversion rate of 0.8 mmol g-1 h-1 with 46% selectivity of C2H6. Detailed characterizations and DFT calculation studies reveal that the introduced Ov sites on Au/ZnAl-v are able to activate O2, and the resulting superoxide radical O2·- greatly promotes the activation of CH4. The coupling of CH3· groups with the assistance of Au cocatalyst leads to the formation of C2H6 with high photocatalytic activity.

Smart Doped Polyaniline Coating for Wireless Anodic Protection of AISI 304 Stainless Steel in a Corrosive Medium Containing Sulfate and Chloride Ions: Electrochemical and DFT Evaluations

Polyaniline (PANI) coatings have the capability of in situ anodic protection of stainless steels (SSs). However, these coatings have a high degradation rate in sulfuric acid. Also, the protection of SSs in a medium contaminated with chloride ions is an unsolved challenge. Therefore, the present work aims to modify the electrodeposited PANI coating with different dopants to find the optimal coating for the anodic protection of 304 SS in chloride-contaminated sulfuric acid. Thus, CH3COO-, HSO4-, NO3-, H2PO4-, and NaSO4- were doped electrochemically in PANI to determine the most effective corrosion depressor. Density functional theory (DF)T calculations determined that the lowest Gibbs free energy (more spontaneous doping) is for HSO4- doping by 24 kcal/mol. The band gap energy is <0.5 eV for the PANI/H2SO4 coating, indicating the very high conductivity of this coating. Monte Carlo simulation revealed that the highest deformation energy is related to PANI/H2SO4 at 1877 kcal/mol (stronger adsorption). Mott-Schottky and energy-dispersive spectroscopy (EDS) results showed that PANI doped with sulfuric acid creates a p-type semiconductor (Ni-rich), while the rest of the dopants lead to the formation of an n-type semiconductor passive film (Fe/Cr-rich). Despite the relatively low corrosion resistance of PANI/H2SO4 in the early days, its resistance improved over time by more than 1 order of magnitude. Therefore, this seems to be a more favorable option for long-term anodic protection. Thus, in this work, the corrosion behavior of the passive film formed at the interface of PANI and SS was comprehensively evaluated.

Perovskite CoSn(OH)6 nanocubes with tuned d-band states towards enhanced oxygen evolution reactions

The CoSn(OH)6 perovskite hydroxide is a structure stable and inexpensive electrocatalyst for the oxygen evolution reaction (OER). However, the OER activity of CoSn(OH)6 is still unfavorable due to its limited active sites. In this work, an Fe3+ doping strategy is used to optimize the d-band state of the CoSn(OH)6 perovskite hydroxide. The CoSn(OH)6 catalyst with slightly Fe3+ doped nanocubes is synthesized by a facile hydrothermal method. Structure characterization shows that Fe3+ ions are incorporated into the crystal structure of CoSn(OH)6. Owing to the regulation of the electronic structure, CoSn(OH)6-Fe1.8% exhibits an OER overpotential of 289 mV at a current density of 10 mA cm-2 in OER electrochemical tests. In situ Raman spectroscopy shows that no obvious re-construction occurred during the OER for both CoSn(OH)6 and CoSn(OH)6-Fe1.8%. DFT calculations show that the introduction of Fe3+ into CoSn(OH)6 can shift the d-band center to a relatively high position, thus promoting the OER intermediates' adsorption ability. Further DFT calculations suggest that incorporation of an appropriate amount of Fe3+ into CoSn(OH)6 significantly reduces the rate-determining Gibbs free energy during the OER. This work offers valuable insights into tuning the d-band center of perovskite hydroxide materials for efficient OER applications.

Strong Interface Coupling Enables Stability of Amorphous Meta-Stable State in CoS/Ni3S2 for Efficient Oxygen Evolution

Rational design of heterostructure catalysts through phase engineering strategy plays a critical role in heightening the electrocatalytic performance of catalysts. Herein, a novel amorphous/crystalline (a/c) heterostructure (a-CoS/Ni3S2) is manufactured by a facile hydrothermal sulfurization method. Strikingly, the interface coupling between amorphous phase (a-CoS) and crystalline phase (Ni3S2) in a-CoS/Ni3S2 is much stronger than that between crystalline phase (c-CoS) and crystalline phase (Ni3S2) in crystalline/crystalline (c/c) heterostructure (c-CoS/Ni3S2) as control sample, which makes the meta-stable amorphous structure more stable. Meanwhile, a-CoS/Ni3S2 has more S vacancies (Sv) than c-CoS/Ni3S2 because of the presence of an amorphous phase. Eventually, for the oxygen evolution reaction (OER), the a-CoS/Ni3S2 exhibits a significantly lower overpotential of 192 mV at 10 mA cm-2 compared to the c-CoS/Ni3S2 (242 mV). An exceptionally low cell voltage of 1.51 V is required to achieve a current density of 50 mA cm-2 for overall water splitting in the assembled cell (a-CoS/Ni3S2 || Pt/C). Theoretical calculations reveal that more charges transfer from a-CoS to Ni3S2 in a-CoS/Ni3S2 than in c-CoS/Ni3S2, which promotes the enhancement of OER activity. This work will bring into play a fabrication strategy of a/c catalysts and the understanding of the catalytic mechanism of a/c heterostructures.

Crystal-Phase-Engineered High-Entropy Alloy Aerogels for Enhanced Ethylamine Electrosynthesis from Acetonitrile

Crystal-phase engineering that promotes the rearrangement of active atoms to form new structural frameworks achieves excellent result in the field of electrocatalysis and optimizes the performance of various electrochemical reactions. Herein, for the first time, it is found that the different components in metallic aerogels will affect the crystal-phase transformation, especially in high-entropy alloy aerogels (HEAAs), whose crystal-phase transformation during annealing is more difficult than medium-entropy alloy aerogels (MEAAs), but they still show better electrochemical performance. Specifically, PdPtCuCoNi HEAAs with the parent phase of face-centered cubic (FCC) PdCu possess excellent 89.24% of selectivity, 746.82 mmol h-1 g-1 cat. of yield rate, and 90.75% of Faraday efficiency for ethylamine during acetonitrile reduction reaction (ARR); while, maintaining stability under 50 h of long-term testing and ten consecutive electrolysis cycles. The structure-activity relationship indicates that crystal-phase regulation from amorphous state to FCC phase promotes the atomic rearrangement in HEAAs, thereby optimizing the electronic structure and enhancing the adsorption strength of reaction intermediates, improving the catalytic performance. This study provides a new paradigm for developing novel ARR electrocatalysts and also expands the potential of crystal-phase engineering in other application areas.

Biphase Pd Nanosheets with Atomic-Hybrid RhOx/Pd Amorphous Skins Disentangle the Activity-Stability Trade-Off in Oxygen Reduction Reaction

The activity-stability trade-off relationship of oxygen reduction reaction (ORR) is a tricky issue that strikes the electrocatalyst population and hinders the widespread application of fuel cells. Here neoteric biphase Pd nanosheets that are structured with ultrathin two-dimensional crystalline Pd inner cores and ≈1 nm thin atomic-hybrid RhOx/Pd amorphous skins, named c/a-Pd@PdRh NSs, for disentangling this trade-off dilemma for alkaline ORR are developed. The superthin amorphous skins significantly amplify the quantity of flexibly low-coordinated atoms for electrocatalysis. An in situ selected oxidation of the top-surface Rh dopants creates atomically hybrid RhOx/Pd disorder surfaces. Detailed energy spectra and theoretical simulation confirm that these RhOx/Pd interfaces can arouse a surface charge redistribution, causing significant electron deficiency and lowered d-band center for surface Pd. Meanwhile, anticorrosive Rh/RhOx species can thermodynamically passivate the neighboring Pd atoms from oxidative dissolution. Thanks to these amplified interfacial effects, the biphase c/a-Pd@PdRh NSs simultaneously exhibit a superhigh ORR activity (5.92 A mg-1, 22.8 times that of Pt/C) and an outstanding long-lasting stability after 100k cycles of accelerated durability test, showcasing unprecedented electrocatalysts for breaking the activity-stability trade-off relationship of ORR. This work paves a bran-new strategy for designing high-performance electrocatalysts through creating modulated amorphous skins on low-dimensional nanomaterials.

3D Noble-Metal Nanostructures Approaching Atomic Efficiency and Atomic Density Limits

Noble metals have been widely used in catalysis, however, the scarcity and high cost of noble metal motivate researchers to balance the atomic efficiency and atomic density, which is formidably challenging. This article proposes a robust strategy for fabricating 3D amorphous noble metal-based oxides with simultaneous enhancement on atomic efficiency and density with the assistance of atomic channels, where the atomic utilization increases from 18.2% to 59.4%. The unique properties of amorphous bimetallic oxides and formation of atomic channels have been evidenced by detailed experimental characterizations and theoretical simulations. Moreover, the universality of the current strategy is validated by other binary oxides. When Cu2IrOx with atomic channels (Cu2IrOx-AE) is used as catalyst for oxygen evolution reaction (OER), the mass activity and turnover frequency value of Cu2IrOx-AE are 1-2 orders of magnitude higher than CuO/IrO2 and Cu2IrOx without atomic channels, largely outperforming the reported OER catalysts. Theoretical calculations reveal that the formation of atomic channels leads to various Ir sites, on which the proton of adsorbed *OH can transfer to adjacent O atoms of [IrO6]. This work may attract immediate interest of researchers in material science, chemistry, catalysis, and beyond.

Modulating Electronic Structure by Etching Strategy to Construct NiSe2 /Ni0.85 Se Heterostructure for Urea-Assisted Hydrogen Evolution Reaction

Exploring and developing novel strategies for constructing heterostructure electrocatalysts is still challenging for water electrolysis. Herein, a creative etching treatment strategy is adopted to construct NiSe2 /Ni0.85 Se heterostructure. The rich heterointerfaces between NiSe2 and Ni0.85 Se emerge strong electronic interaction, which easily induces the electron transfer from NiSe2 to Ni0.85 Se, and tunes the charge-state of NiSe2 and Ni0.85 Se. In the NiSe2 /Ni0.85 Se heterojunction nanomaterial, the higher charge-state Ni0.85 Se is capable of affording partial electrons to combine with hydrogen protons, inducing the rapid formation of H2 molecule. Accordingly, the lower charge-state NiSe2 in the NiSe2 /Ni0.85 Se heterojunction nanomaterial is more easily oxidized into high valence state Ni3+ during the oxygen evolution reaction (OER) process, which is beneficial to accelerate the mass/charge transfer and enhance the electrocatalytic activities towards OER. Theoretical calculations indicate that the heterointerfaces are conducive to modulating the electronic structure and optimizing the adsorption energy toward intermediate H* during the hydrogen evolution reaction (HER) process, leading to superior electrocatalytic activities. To expand the application of the NiSe2 /Ni0.85 Se-2h electrocatalyst, urea is served as the adjuvant to proceed with the energy-saving hydrogen production and pollutant degradation, and it is proven to be a brilliant strategy.

Unlocking the Potential of Amorphous Prussian Blue with Highly Active Mn Sites at Room Temperature for Impressive Oxygen Evolution Reaction and Super Capacitor Electrochemical Performance

The key to increasing the rate of oxygen evolution reaction (OER) lies in accelerated four-electron dynamics, while the key to facilitating the development of supercapacitors lies in the design of electrode materials. This paper synthesized manganese-iron Prussian blue (MnFe-PBA@IF) at room temperature, and hexagonal concave structures w ere prepared using a fast-reducing matrix. Interestingly, MnFe-PBA@IF has an amorphous structure favorable to exposing more active surfaces. According to Gibbs free energy calculations on MnFe-PBA, charge depletion of manganese atoms can greatly enhance the adsorption of electron-rich oxygen-containing groups on the surface. Furthermore, the overpotential in 1 m KOH is 280 mV. Also, it can be used as a supercapacitor with a stable operating voltage range of -0.9-0 V and a specific capacity of 1260 F g-1 . This work provides new insights into the synthesis of OER catalysts for Prussian blue ferromanganese at room temperature. Non-gold-bonded adsorption, highly active metal centers and active surfaces are the underlying reasons for the superior performance of supercapacitors. Therefore, Prussian blue with good energy storage performance and high active surface can be used as multifunctional energy storage and conversion electrodes.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Metastable Hexagonal-Phase Nickel with Ultralow Pt Content for an Efficient Alkaline/Seawater Hydrogen Evolution Reaction

Hydrogen has been hailed as the core of the world's future energy architecture. It is imperative to develop catalysts with an efficient and sustained hydrogen evolution reaction (HER) to scale up alkaline/seawater electrolysis, yet significant difficulties and challenges, such as the high usage of precious metals, still remain. In this paper, a metastable-phase hexagonal close-packed (hcp) Ni-based catalyst with ultralow Pt content (3.1 at %) was designed, which has excellent catalytic performance in the alkaline/seawater HER. The optimal catalyst offers low overpotentials of 21 and 137 mV at 10 mA cm-2 and remains stable during operation for 100 and 300 h at this current density in 1.0 M KOH and real seawater, respectively. A mechanistic study shows that the metastable-phase Ni acts as an anchor site for OH-, which promotes the dissociation of water and greatly improves the formation rate of H2.

Insight into selenium vacancies enhanced CoSe2/MoSe2 heterojunction nanosheets for hydrazine-assisted electrocatalytic water splitting

The integration of interface engineering and vacancy engineering was a feasible way to develop highly efficient electrocatalysts toward water electrolysis. Herein, we designed CoSe2/MoSe2 heterojunction nanosheets with abundant Se vacancies (VSe-CoSe2/MoSe2) for electrocatalytic water splitting. In the VSe-CoSe2/MoSe2 electrocatalyst, the electrons more easily transferred from CoSe2 to MoSe2, and interface engineering not only modulated the electronic structure, but also supplied more heterointerfaces and catalytic sites. After chemical etching, partial Se atoms were eliminated, which further activated the inert plane of the VSe-CoSe2/MoSe2 electrocatalyst and induced electron redistribution. The removal of surface Se atoms was also beneficial to expose inner reactive sites, which promoted adsorption toward reaction intermediates. Density functional theory calculations revealed that interface engineering and vacancy engineering collaboratively optimized the adsorption energy of the VSe-CoSe2/MoSe2 electrocatalyst toward the intermediate H* during the hydrogen evolution reaction process, leading to better electrocatalytic activity. The density of state diagram manifested the refined electronic structure of the VSe-CoSe2/MoSe2 electrocatalyst, and it exhibited a higher electronic state near the Fermi level, which indicated superior electronic conductivity, facilitating electron transport during the catalytic process. In alkaline media, the VSe-CoSe2/MoSe2 electrocatalyst delivered low overpotentials of merely 74 and 242 mV to obtain 10 mA cm-2 toward hydrogen evolution reaction and oxygen evolution reaction. This work illustrated the feasibility of combining two or more strategies to develop high-performance catalysts for water electrolysis.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

Flower-Like Amorphous MoO3- x Stabilized Ru Single Atoms for Efficient Overall Water/Seawater Splitting

Benefitting from the maximum atom utilization efficiency, special size quantum effects and tailored active sites, single-atom catalysts (SACs) have been promising candidates for bifunctional catalysts toward water splitting. Besides, due to the unique structure and properties, some amorphous materials have been found to possess better performance than their crystalline counterparts in electrocatalytic water splitting. Herein, by combining the advantages of ruthenium (Ru) single atoms and amorphous substrates, amorphous molybdenum-based oxide stabilized single-atomic-site Ru (Ru SAs-MoO3- x /NF) catalysts are conceived as a self-supported electrode. By virtue of the large surface area, enhanced intrinsic activity and fast reaction kinetics, the as-prepared Ru SAs-MoO3- x /NF electrode effectively drives both oxygen evolution reaction (209 mV @ 10 mA cm-2 ) and hydrogen evolution reaction (36 mV @ 10 mA cm-2 ) in alkaline media. Impressively, the assembled electrolyzer merely requires an ultralow cell voltage of 1.487 V to deliver the current density of 10 mA cm-2 . Furthermore, such an electrode also exhibits a great application potential in alkaline seawater electrolysis, achieving a current density of 100 mA cm-2 at a low cell voltage of 1.759 V. In addition, Ru SAs-MoO3- x /NF only has very small current density decay in the long-term constant current water splitting test.

Crystallinity engineering for overcoming the activity-stability tradeoff of spinel oxide in Fenton-like catalysis

A precise modulation of heterogeneous catalysts in structural and surface properties promises the development of more sustainable advanced oxidation water purification technologies. However, while catalysts with superior decontamination activity and selectivity are already achievable, maintaining a long-term service life of such materials remains challenging. Here, we propose a crystallinity engineering strategy to break the activity-stability tradeoff of metal oxides in Fenton-like catalysis. The amorphous/crystalline cobalt-manganese spinel oxide (A/C-CoMnOx) provided highly active, hydroxyl group-rich surface, with moderate peroxymonosulfate (PMS)-binding affinity and charge transfer energy and strong pollutant adsorption, to trigger concerted radical and nonradical reactions for efficient pollutant mineralization, thereby alleviating the catalyst passivation by oxidation intermediate accumulation. Meanwhile, the surface-confined reactions, benefited from the enhanced adsorption of pollutants at A/C interface, rendered the A/C-CoMnOx/PMS system ultrahigh PMS utilization efficiency (82.2%) and unprecedented decontamination activity (rate constant of 1.48 min-1) surpassing almost all the state-of-the-art heterogeneous Fenton-like catalysts. The superior cyclic stability and environmental robustness of the system for real water treatment was also demonstrated. Our work unveils a critical role of material crystallinity in modulating the Fenton-like catalytic activity and pathways of metal oxides, which fundamentally improves our understanding of the structure-activity-selectivity relationships of heterogeneous catalysts and may inspire material design for more sustainable water purification application and beyond.

Lamella-heterostructured nanoporous bimetallic iron-cobalt alloy/oxyhydroxide and cerium oxynitride electrodes as stable catalysts for oxygen evolution

Developing robust nonprecious-metal electrocatalysts with high activity towards sluggish oxygen-evolution reaction is paramount for large-scale hydrogen production via electrochemical water splitting. Here we report that self-supported laminate composite electrodes composed of alternating nanoporous bimetallic iron-cobalt alloy/oxyhydroxide and cerium oxynitride (FeCo/CeO_2-xN_x) heterolamellas hold great promise as highly efficient electrocatalysts for alkaline oxygen-evolution reaction. By virtue of three-dimensional nanoporous architecture to offer abundant and accessible electroactive CoFeOOH/CeO_2-xN_x heterostructure interfaces through facilitating electron transfer and mass transport, nanoporous FeCo/CeO_2-xN_x composite electrodes exhibit superior oxygen-evolution electrocatalysis in 1 M KOH, with ultralow Tafel slope of ~33 mV dec^-1. At overpotential of as low as 360 mV, they reach >3900 mA cm^-2 and retain exceptional stability at ~1900 mA cm^-2 for >1000 h, outperforming commercial RuO₂ and some representative oxygen-evolution-reaction catalysts recently reported. These electrochemical properties make them attractive candidates as oxygen-evolution-reaction electrocatalysts in electrolysis of water for large-scale hydrogen generation.

Insights into an Amorphous NiCoB Nanoparticle-Catalyzed MgH2 System for Hydrogen Storage

In the paper, we synthesized amorphous NiCoB nanoparticles by a simple chemical reduction method and employed them as high-activity catalysts to considerably improve the hydrogen storage properties of MgH₂. The MgH₂-NiCoB composite quickly absorbed 3.6 wt % H₂ at a low temperature of 85 °C and released 5.5 wt % H₂ below 270 °C within 600 s. It is worth noting that the hydrogenation activation energy was reduced to 33.0 kJ·mol^-1. Detailed microstructure analysis reveals that MgB₂, Mg₂Ni/Mg₂NiH₄, and Mg₂Co/Mg₂CoH₅ were in situ generated during the first de/absorption cycle and dispersed at the surface of NiCoB. These active ingredients created lots of boundary interfaces to facilitate the hydrogen diffusion and destabilize the Mg-H bonds, thus decreasing the kinetic barriers. This work provides support for a promising catalytic effect of amorphous NiCoB on de/absorption reactions of MgH₂, showing new ways for designing Mg-based hydrogen storage systems toward practical application.

Spinel-Derived Formation and Amorphization of Bimetallic Oxyhydroxides for Efficient Electrocatalytic Biomass Oxidation

Replacing the oxygen evolution reaction (OER) with water-assisted oxidation of organic molecules represents a promising approach for achieving sustainable electrochemical biomass utilization. Among numerous OER catalysts, spinels have received substantial attention due to their manifold compositions and valence states, yet their application in biomass conversions remains rare. Herein, a series of spinels were investigated for the selective electrooxidation of furfural and 5-hydroxymethylfurfural, two model substrates for versatile value-added chemical products. Spinel sulfides universally exhibit superior catalytic performance compared to that of spinel oxides, and further investigations show that the replacement of oxygen with sulfur led to the complete phase transition of spinel sulfides into amorphous bimetallic oxyhydroxides during electrochemical activation, serving as the active species. Excellent values of conversion rate (100%), selectivity (100%), faradaic efficiency (>95%), and stability were achieved via sulfide-derived amorphous CuCo-oxyhydroxide. Furthermore, a volcano-like correlation was established between their BEOR and OER activities based on an OER-assisted organic oxidation mechanism.

Heterointerface and Tensile Strain Effects Synergistically Enhances Overall Water-Splitting in Ru/RuO2 Aerogels

Designing robust electrocatalysts for water-splitting is essential for sustainable hydrogen generation, yet difficult to accomplish. In this study, a fast and facile two-step technique to synthesize Ru/RuO₂ aerogels for catalyzing overall water-splitting under alkaline conditions is reported. Benefiting from the synergistic combination of high porosity, heterointerface, and tensile strain effects, the Ru/RuO₂ aerogel exhibits low overpotential for oxygen evolution reaction (189 mV) and hydrogen evolution reaction (34 mV) at 10 mA cm^-2 , surpassing RuO₂ (338 mV) and Pt/C (53 mV), respectively. Notably, when the Ru/RuO₂ aerogels are applied at the anode and cathode, the resultant water-splitting cell reflected a low potential of 1.47 V at 10 mA cm^-2 , exceeding the commercial Pt/C||RuO₂ standard (1.63 V). X-ray adsorption spectroscopy and theoretical studies demonstrate that the heterointerface of Ru/RuO₂ optimizes charge redistribution, which reduces the energy barriers for hydrogen and oxygen intermediates, thereby enhancing oxygen and hydrogen evolution reaction kinetics.

A "Special" Solvent to Prepare Alloyed Pd2Ni1 Nanoclusters on a MWCNT Catalyst for Enhanced Electrocatalytic Oxidation of Formic Acid

Herein, an electrocatalyst with Pd₂Ni₁ nanoclusters, supporting multiwalled carbon nanotubes (MWCNTs) (referred to Pd₂Ni₁/CNTs), was fabricated with deep eutectic solvents (DES), which simultaneously served as reducing agent, dispersant, and solvent. The mass activity of the catalyst for formic acid oxidation reaction (FAOR) was increased nearly four times compared to a Pd/C catalyst. The excellent catalytic activity of Pd₂Ni₁/CNTs was ascribed to the special nanocluster structure and appropriate Ni doping, which changed the electron configuration of Pd to reduce the d-band and to produce a Pd-Ni bond as a new active sites. These newly added Ni sites obtained more OH^- to release more effective active sites by interacting with the intermediate produced in the first step of FAOR. Hence, this study provides a new method for preparing a Pd-Ni catalyst with high catalytic performance.

Volcano relationships and a new activity descriptor of 2D transition metal-Fe layered double hydroxides for efficient oxygen evolution reaction

Iron (Fe) sites play a critical role in boosting the catalytic activity of transition metal layered double hydroxide (LDH) electrocatalysts for the oxygen evolution reaction (OER), but the contribution of the Fe content to the catalysis of Fe-doped LDHs is still not well understood. Herein, a series of two-dimensional (2D) Fe-doped MFe-LDHs (M = Co, Ni, Cu, and Mn) was synthesized via a general molecular self-assembly method to track the role of Fe in their electrocatalytic OER activities. Besides the revelation of the intrinsic activity trend of NiFe > CoFe > MnFe > CuFe, volcano-shaped relationships among the catalytic activity descriptors, i.e., overpotential, Tafel slope, and turnover frequency (TOF), and the Fe-content in MFe-LDHs, were identified. Specifically, a ∼20% Fe content resulted in the highest OER performance for the LDH, while excess Fe compromised its activity. A similar volcano relationship was determined between the intermediate adsorption and Fe content via operando impedance spectroscopy (EIS) measurements, and it was shown that the intermediate adsorption capacitance (CPE_ad) can be a new activity descriptor for electrocatalysts. In this work, we not only performed a systematic study on the role of Fe in 2D Fe-doped LDHs but also offer some new insights into the activity descriptors for electrocatalysts.

Identification of the Origin for Reconstructed Active Sites on Oxyhydroxide for Oxygen Evolution Reaction

The regulation of atomic and electronic structures of active sites plays an important role in the rational design of oxygen evolution reaction (OER) catalysts toward electrocatalytic hydrogen generation. However, the precise identification of the active sites for surface reconstruction behavior during OER remains elusive for water-alkali electrolysis. Herein, irreversible reconstruction behavior accompanied by copper dynamic evolution for cobalt iron layered double hydroxide (CoFe LDH) precatalyst to form CoFeCuOOH active species with high-valent Co species is reported, identifying the origin of reconstructed active sites through operando UV-Visible (UV-vis), in situ Raman, and X-ray absorption fine-structure (XAFS) spectroscopies. Density functional theory analysis rationalizes this typical electronic structure evolution causing the transfer of intramolecular electrons to form ligand holes, promoting the reconstruction of active sites. Specifically, unambiguous identification of active sites for CoFeCuOOH is explored by in situ ¹⁸ O isotope-labeling differential electrochemical mass spectrometry (DEMS) and supported by theoretical calculation, confirming mechanism switch to oxygen-vacancy-site mechanism (OVSM) pathway on lattice oxygen. This work enables to elucidate the vital role of dynamic active-site generation and the representative contribution of OVSM pathway for efficient OER performance.

Axial Phosphate Coordination in Co Single Atoms Boosts Electrochemical Oxygen Evolution

Cobalt single atoms coordinated with planar four nitrogen atoms (Co₁ N₄ ) represent an efficient electrocatalyst for oxygen evolution reaction (OER), whereas the large energy barrier of CoOH dehydrogenation limits the OER activity. Herein, axial phosphate (PO₄ ) coordination is incorporated in Co₁ N₄ single atoms of cobalt phthalocyanine@carbon nanotubes (P-CoPc@CNT), so as to boost the intrinsic OER performance through manipulating the reaction pathway. With a relative low mass loading of Co (2.7%), the P-CoPc@CNT shows remarkable alkaline OER activity with the overpotential of 300 mV and Tafel slope of 41.7 mV dec^-1 , which dramatically outperforms the CoPc@CNT without axial PO₄ coordination. Based on mechanistic analysis, the axial PO₄ coordination directly participates in the OER cycle by the transformation of axial ligand. Specially, the CoOH dehydrogenation process is replaced by the dehydrogenation of HPO₄ -Co₁ N₄ intermediate, which largely decreases the energy barrier and thus benefits the whole OER process.

Abundant Dislocation Layered Double Hydroxides Synthesis by Molten Salt with Bound Water Boosting Oxygen Evolution

Optimizing the adsorption free energy and promoting the active phase transition to further enhance the oxygen evolution reaction (OER) activity remain significant challenges. The adsorption free energy can be optimized by modulating the electronic structure and adjusting the crystal configuration. Meanwhile, the transformation of the active phase can be promoted by introducing strain energy. The theoretical calculations are conducted to verify the rational envisage. However, it is still a great obstacle to introducing strain into the electrocatalysts and avoiding destruction. The stress field caused by dislocation can realize both of the above. Hence, the molten salt with the bound water method is proposed and the abundant dislocation layered double hydroxides (D-NiFe LDH) are constructed. The in situ characterizations further verify the dislocations significantly affect the generation of the active phase and the state of electronic structure. Consequently, the D-NiFe LDH exhibits outstanding OER activity and obtains 10 mA cm^-2 , only requiring 199 mV overpotential with fabulous stability (100 mA cm^-2 more than 24 h). The work paves a new avenue for the rational introduction dislocations to optimize the crystal configuration and boost the active phase formation, significantly enhancing the OER performance.

Hollow-structured amorphous Cu(OH)x nanowires doped with Ru for wide pH electrocatalytic hydrogen production

Developing efficient and stable catalysts for electrocatalytic hydrogen evolution reaction (HER) with low overpotential is the key point to realizing large-scale hydrogen commercialization. Herein, Ru doped amorphous hollow copper hydroxide nanowires on copper foam (Ru-Cu(OH)_x/CF) is prepared by surface chemical oxidization and following solvothermal process. The hollow 3D nanowire structure can provide abundant accessibility active sites, promote electrolyte in filtration and facilitate gas diffusion in the process of the electrochemical reaction. Then, the as-synthesized Ru-Cu(OH)_x/CF electrocatalyst exhibits impressive electrocatalytic performance for HER with 45, 80 and 50 mV to drive 10 mA cm^-2 in 1.0 M KOH, 1.0 M phosphate-buffered saline (PBS) and 0.5 M H₂SO₄, respectively, with remarkable long-term stability. Moreover, sustainable energies can power the two-electrode setup with amounts of hydrogen generation. The strategy may be particularly beneficial to explore simple synthesis and high-performance catalysts for HER.

Stannate-catalysed glucose-fructose isomerisation in alcohols

Isomerisation of glucose to fructose is a crucial step in the valorisation of biomass-derived carbohydrates to renewable chemicals, polymers and fuels. Glucose isomerisation is base-catalysed but superior catalytic activity can...